1. Field of the Invention
The present invention generally relates to intra-train communications, and more particularly to a system and method for communicating data between a head unit in a lead locomotive and one or more trailing units which operate in accordance with different data protocols.
2. Background Description
Wireless communications systems have been developed for improving the command and control response time of a train. These systems typically include an end-of-train (EOT) unit containing a telemetry transmitter attached to the last car of a train in the place of a caboose, and a computer commonly referred to as a locomotive control unit (LCU) or head-of-train unit installed in the lead locomotive.
EOT units perform three principal functions. First, they monitor various operating conditions of the train including air pressure in the brake line, battery condition, marker light condition, motion, and emergency valve status. EOT units also perform marker light operations and monitor train movement, at least in the rear portion of the train. Second, EOT units transmit the information they monitor to a lead locomotive so that informed command and control decisions may be taken. And Third, the EOT provides the ability to vent air from the brake pipe at the rear of the train in the event of an emergency.
Originally, EOT units were one-way systems, i.e., data was only transmitted from the EOT unit to the LCU where it was then displayed. These one-way units have proven inadequate in a number of ways. Perhaps most importantly, in a one-way system, emergency application of the brakes begins at the lead locomotive and slowly progresses along the train brake pipe until the final car is reached. This sequential application of the brakes increases the time and distance required for the train to come to a complete stop, especially for long train consists. Furthermore, if a blockage or restriction were present in the brake pipe, the brakes beyond the restriction may not engage, increasing the possibility of a derailment and consequently loss of life and property.
Recently, two-way EOT units have been developed which transmit and receive data to and from the LCU. In addition to performing passive monitoring functions, two-way EOT units control air valves in the brake line to effect emergency braking in response to control signals sent from the LCU. The ability to perform a braking application at the rear of the train simultaneously with braking at the front of the train reduces the time and distance required for the train to come to a stop, and thus in at least this way development of two-way EOT units has represented a substantial improvement in the art. An intra-train communications system employing a two-way EOT unit is disclosed in U.S. Pat. No. 5,720,455.
Before command data can be communicated between the LCU and a two-way EOT, a communications link must be established. This link is formed using a communications protocol based on, for example, a handshaking procedure as disclosed in U.S. Pat. No. 4,582,280. In order for emergency commands to be communicated to the EOT unit over this link, the LCU must first be "armed" so that it transmits these commands only to the EOT unit attached to the train. This is desirable in order to prevent the LCU from mistakenly engaging the emergency brakes in other trains which happen to pass by. Arming procedures of this type are disclosed, for example, in U.S. Pat. Nos. 5,374,015 and 5,377,938.
Numerous command protocols are presently in use for communicating data between the LCU and EOT of a train. One of the most common protocols is one approved by the Association of American Railroads (AAR). The AAR protocol transmits digital data using Minimum Shift Keying (MSK) modulation (with mark and space frequencies of 1200 and 1800 Hz, respectively) within a UHF frequency band. Typically, 452.9375 MHz is used for the front-to-rear channel and 457.9375 MHz for the rear-to-front channel. The rear-to-front channel consists of a Unit ID, rear brake pipe pressure, marker light status, last car motion and optional directional status, EOT emergency valve status, and a BCH error detection code. The front-to-read data consists of a Unit ID, a command byte signifying either a communication test command or EOT emergency brake application command, and a BCH error detection code. The arming information on the AAR system resides in the LCU.
Other protocols for communicating data between an LCU and EOT are different from the AAR protocol in terms of the frequency bands over which they operate (i.e., other than the UHF band), the types of digital modulation techniques employed, and the arming procedures used.
With recent consolidation in the railroad industry, it is increasingly the case that trains are being assembled with LCUs and EOTs that operate using different protocols, at least for a portion of their journey. For example, a train configured with an AAR LCU and AAR EOT may be modified to include an EOT operating in accordance with another protocol at some point in an intermediate train yard. This presents compatibility problems, since unless some protocol conversion takes place the LCU and EOT will not be able to communicate with one another.
One system has been proposed to solve this compatibility problem. In this system, an LCU is used which translates between two protocols. This LCU, however, has proven inadequate in at least three ways. First, this system performs protocol conversions solely as the result of manual operations. This system, for example, has a switch on a front panel of the LCU which is manually set by the operator for configuring the LCU so that the protocol conversion can take place.
Second, this manual system requires the IFC software to be either re-programmed or changed to handle differences in the arming procedure. If these software changes are not made, IFC operation would be inconsistent with the EOT operation, which could potentially prevent the system from arming properly.
Third, this manual system is highly susceptible to malfunctioning because of operator error. For example, such a system is potentially dangerous because if the switch on the LCU panel were changed to the wrong setting no communications would take place between the LCU and EOT. As a result, emergency application of the brakes would not be performed at the rear of the train, despite the fact that the IFC would still indicate that the emergency function was available.
A need therefore exists for an improved system and method for resolving the compatibility problems that exist between a head unit and an EOT unit of a train which operate using different protocols, and more particularly one which is more convenient to use and which operates with greater reliability and efficiency compared with conventional systems.